Marcus,
My squamosa seems to like a lot of light, it's under a 400 watt XM20k bulb at the bottom of a 24" deep tank and it stays spread out during the day like it wants more light. That said, people do have success with squamosa's with less light than would be required for a maxima or crocea for example. As far as maintaning your calcium levels, you also should keep up your alkalinity and keep a steady PH. If you don't keep your alkalinity >= to NSW levels clams can't build there shells. Squamosa's grow quick. The clam pictured in my post above has grown from 5" to 11" in about a year. Randy in the chemistry forum has written some good articles on how to maintain calcium and alkalinity.
Brent